Unfortunately (for them), they were not terribly clear in their assumptions;
as a result, they have made several mistakes which call their conclusions
into question. I shall begin where they end, with their technical
calculation.

[1] The lack of units in the calculation is in the original. This is
an omission, not an error; if filled in, they would be:
108 MTOE/yr * 1000 kt/mt * 11.63 GWH/kt * 1000 MWH/GWH / (365 days/yr * 24 hr/day) = 143,000 MW
[2] The conversion factor 11.63 GWH/kt (equivalent to 11.63 KWH/kg) appears to be a bit high, but not unreasonably so. They got it from a fact sheet available here.

What's wrong with that?

There are several minor errors and two major errors in this
calculation. The major errors dwarf the others into irrelevance:

In (2), they assume that conversion to hydrogen is the best, or only, way to
make renewable energy available to power transport.

Throughout, they assume that the conversion of oil to work is 100% efficient.

The first assumption is debatable, the second is absurd. The
efficiency of typical diesel truck engines peaks out around 40% and
averages considerably less; the efficiency of automobiles is much
lower still, around 17% in the USA.

Trying to get it right

If we make an effort to correct their assumptions by:

accounting for the losses of current engines by assuming an average
efficiency of 25%, and

assuming that most power is stored in batteries at 70% efficiency
instead of hydrogen at 50% efficiency,

This reduces the requirements from a 10 km strip of wind plants around
Britain to 2 km (assuming no improvements there either; the news just
came of a 126-meter wind turbine capable of 5 MW peak, which would cut
the number and depth still more) or 24 nuclear plants at 1100 MW each
instead of 100.

That's still a hell of a lot. Nobody said it was going to be a
trivial job, but it's nowhere near as big as the Oswalds make
it out to be.

There are better scenarios. If you assume that rainy, foggy Britain
gets 300 W/m^2 of sunlight for 6 hours on the average day and you've
got solar panels at 15% efficiency, that 25,600 MW of average power
could be met with a bit over 2,200 km2 of area; if you can
get to 50% efficiency using ballistic-electron quantum dot cells, the
requirement is a mere 683 km^2. Do roofs and pavement on the
island cover 3.4% of the area of Wales yet?
If they do, the impenetrable wall of wind turbines turns into faux
slate tiles and the problem literally vanishes into the background.
Such are the tradeoffs.
¶ 10/08/2004 11:02:00 PM7 commentslinks to this post

Talk largely about energy and work, but also politics and other random thoughts